So, the stranger, no backstory right? So imagine this, if she doesn't show up in TTK. All of the things shes known about what is needing to happen in our world of Destiny. What if she's recreated the vex tech in Destiny 2 after we've destroyed it in our game. She isn't a guardian, but she may have been built by or taught by an old living guardian after another dark age because of either a new threat, or we failed to completely kill Oryx and he's completely Taken over everything after coming back (pun intended) and she came back with the recreated lost vex tech to try and prevent everything